The purpose of this research is to delineate barriers, pathways and transport mechanisms within the normal and altered cochlea using ultra microscopic investigation. Abnormal conditions will be induced by ototoxic atibiotics, diuretics, acoustic trauma, propylthiouracil, histimine and mechanical alteration of anatomical barriers, and studied by means of electron-microscopically-visible tracers such as horseradish peroxidase and ruthenium red. The object is to delineate compartments of the membranous labyrinth (endolymphatic, perilymphatic, vascular) and the types, amount, and pathways of exchange between these compartment, ultimately to understand the function of the membranous labyrinth, both under normal conditions and in abnorm al states such as endolymphatic hydrops and sudden deafness.